1. Field of the Invention
The present invention relates to a semiconductor device, in particular, a semiconductor device including an oxide semiconductor layer.
It is to be noted that the semiconductor device in this specification refers to all devices that can function by utilizing semiconductor characteristics, and electro-optic devices, semiconductor circuits, and electronic appliances are all semiconductor devices.
2. Description of the Related Art
Attention has been focused on a technique for forming a transistor (also referred to as a thin film transistor (TFT)) using a semiconductor thin film formed over a substrate having an insulating surface. The transistor is applied to a wide range of electronic appliances such as an integrated circuit (IC) or an image display device (display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor, while an oxide semiconductor has been attracting attention as another material.
For example, a transistor including a semiconductor layer formed using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) (In—Ga—Zn—O-based amorphous oxide) is disclosed (see Patent Document 1).